diff --git a/lib/db/postgres7.php b/lib/db/postgres7.php
index acf7e94db3d..2401f418555 100644
--- a/lib/db/postgres7.php
+++ b/lib/db/postgres7.php
@@ -768,6 +768,7 @@ function main_upgrade($oldversion=0) {
         
         // odd! username was missing its unique index!
         // first silently drop it just in case...
+        execute_sql("ALTER TABLE {$CFG->prefix}user DROP CONSTRAINT {$CFG->prefix}user_username_uk;", false);   
         execute_sql("DROP INDEX {$CFG->prefix}user_username_uk", false);
         modify_database('', "CREATE UNIQUE INDEX prefix_user_username_uk ON prefix_user (username);");